The invention relates to a method and apparatus for the direct production of industrial lead oxide, wherein molten lead is fed into a reactor and is stirred with the addition of air and the resulting reaction product is drawn off.
Lead oxide is the starting material or the significant component of various chemical processes and has to satisfy a range of quality requirements which make the production thereof difficult. The basic reaction Pb+1/2O.sub.2 =PbO takes place relatively well at temperatures from 200.degree. C. upwards. However, the degree of conversion of this reaction, by hitherto known methods, is so poor that for the manufacture of a product complying with the required quality, a pre-oxidation process in a first reactor has to be supplemented with a final oxidation in a second process step. Even the so-produced lead oxide is usually not ready for marketing due to its particle size distribution, and has to undergo sifting, grinding or sieving in a third process stage.
Thus a lead oxide complying with marketing demands with more than 99.7% PbO and a maximum particle size of 60 .mu.m, has hitherto had to undergo a very complicated production, and such known methods are costly in connection with capital, energy and personnel requirements.
The method steps of pre-oxidation and final oxidation have undergone development improvements in various ways, and even the device used for the pre-oxidation, known as the Barton reactor, has been changed in order to increase the efficiency and production quality of the product; however a degree of oxidation of 99% in the manufactured product has practically never been exceeded. As disclosed in DE-AS No. 1,467,347 and U.S. Pat. No. 3,322,496, for example, by varying the lead input as well as the air input through introduction of air in the base part of the reaction vessel, by applying a baffle plate in front of the outlet for the reaction product, by interception of a cyclone separator and through back-feeding and further oxidation of the larger and heavier reaction product particles, content of metallic lead in the product under 4% by weight and preferably less than 2% by weight has been achieved. Individual values of samples taken during the process run occasionally exhibit a lead content by weight but under 1%, do not decrease the average value of the Pb content to below 1%. A product with 1% metallic lead content is, however, not acceptable in the most important fields of application such as glass, ceramics and stabilizer industries.
The following systems are known for the control of the reaction in the Barton reactor:
1. PA0 2.
(a) Constant maintenance of the air volume sucked through the reactor, PA1 (b) infeed of the molten lead in small amounts depending on the temperature in the reactor. PA1 (a) Even lead infeed over an average span, PA1 (b) air-control depending on the temperature in the reactor.
In both of these systems, the process runs automatically and on average, a uniform product is produced. This apparent uniformity disappears however, if several instantaneous samples are drawn during a cycle run and then analyzed. Depending on the degree of fluctuation of the reactor temperature, deviations from the average degree of oxidation are found which account for several percentage units. This has no serious effect in a two-stage process, due to the subsequent oxidizing of the product.
Such deviations however, are inadmissible if a practically fully oxidized product is to be produced. During a cycle run a fully oxidized product may be reached, but afterwards an insufficiently oxidized product could occur for a time, and the oxidation of the product would be insufficient.